For protection against attacks by non-conventional weapons such as NBC, there is the sealed room, which replaces the ventilated bomb shelter. Both the sealed room and the bomb shelter present disadvantages. In a sealed room, difficulties are encountered in obtaining tightly sealed doors and windows in order to prevent the penetration of contaminated air. A main disadvantage of bomb shelters is that their ventilation and filtration systems require too much space, are generally fixed in one location, and cannot be easily and quickly relocated.